Fine Tune Oracle Execution Plans for Performance Gains. Janis Griffin Senior DBA

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1 Fine Tune Oracle Execution Plans for Performance Gains Janis Griffin Senior DBA 1

2 Who Am I? Senior DBA for Confio Current Years in Oracle Former Database Design & Implementation Specialize in Performance Tuning Review Database Performance for Customers and Prospects Common Thread How do I tune it? 2

3 Agenda What are Execution Plans How to View Them Interpret Plan Details / Tips / Techniques Tune Case Study Additional Tools 3

4 What are Execution Plans Execution plans provide the sequence of operations performed in order to run SQL Statements. They show: Order of the tables referenced in the statement Access method for each table in the statement INDEX INLIST ITERATOR TABLE ACCESS VIEW Join method in statement accessing multiple tables HASH JOIN MERGE JOIN NESTED LOOPS Data manipulations CONCATENATION COUNT FILTER SORT 4

5 Execution Plan Information 5 Operation - Name of the internal action performed in each step. First Row is always: DELETE STATEMENT INSERT STATEMENT SELECT STATEMENT UPDATE STATEMENT Options Variation of Operation Object_name Table or Index Parent_id Related Operations More Information Not listed here Operation List: AND-EQUAL CONNECT BY CONCATENATION COUNT DOMAIN INDEX FILTER FIRST ROW FOR UPDATE HASH JOIN INDEX ITERATOR INTERSECTION MERGE JOIN MINUS NESTED LOOPS PARTITION REMOTE SEQUENCE SORT TABLE ACCESS UNION VIEW Option Examples: AGGREGATE ALL BY INDEX ROWID BY LOCAL INDEX ROWID BY USER ROWID CARTESIAN FAST FULL SCAN FULL FULL OUTER FULL SCAN GROUP BY ITERATOR ORDER BY OUTER PARTITION RANGE SCAN SAMPLE FAST FULL SCAN SKIP SCAN UNIQUE

6 What are Execution Plans Optimizer s detailed steps to execute a SQL Statement SELECT e.empno EID, e.ename "Employee_name", d.dname "Department, e.hiredate "Hired_Date" FROM emp e, dept d WHERE d.deptno = '40' AND e.deptno = d.deptno; Access Index Scan Id Operation & Option Name SELECT STATEMENT 1 NESTED LOOPS 2 TABLE ACCESS BY INDEX ROWID DEPT 3 INDEX UNIQUE SCAN PK_DEPT 4 TABLE ACCESS FULL EMP Emp Pk_Dept Access Dept Nested Loops 6

7 EXPLAIN PLAN Estimated plan - can be wrong for many reasons Explain Plan For sql statement Set autotrace (on trace exp stat off) V$SQL_PLAN (Oracle 9i+) Actual execution plan Use DBMS_XPLAN for display How To View Plans Tracing (all versions) / TKPROF Get all sorts of good information Works when you know a problem will occur Historical Plans AWR, Confio Ignite Shows plan changes over time DBMS_XPLAN - Table Functions to Format & Display Plans DISPLAY - contents of a plan table. DISPLAY_AWR the plan of a stored SQL statement in AWR. DISPLAY_CURSOR - the execution plan of any loaded cursor. DISPLAY_SQL_PLAN_BASELINE 1+ plans for a SQL statement DISPLAY_SQLSET - multi-plans of statements in SQL tuning set 7

8 DBMS_XPLAN 11g New Functions 11g BUILD_PLAN_XML Return the last plan, or a named plan, explained as XML DISPLAY Shows the last plan explained EXPLAIN PLAN ** Only FUNCTION in Oracle 9i DISPLAY_AWR DISPLAY_CURSOR DISPLAY_PLAN DISPLAY_SQLSET DISPLAY_SQL_PLAN_BASELINE FORMAT_NUMBER FORMAT_NUMBER2 FORMAT_SIZE FORMAT_SIZE2 FORMAT_TIME_S PREPARE_PLAN_XML_QUERY PREPARE_RECORDS VALIDATE_FORMAT Format & display the plan of a stored SQL statement in AWR Format & display the execution plan of any loaded cursor Return the last plan, or a named plan, explained as a CLOB Format & display the execution plan of statements stored in a SQL tuning set Displays one or more plans for the specified SQL statement Returns a number as a string Returns a number as a string formatted with a leading space (CHR(32)) Undocumented Undocumented Undocumented - function to build the XML version of a select query that is run before the display function to retrieve and display the execution plan of a SQL Used Internally Used Internally 8

9 Execution Plan Details SELECT e.empno EID, e.ename "Employee_name, d.dname "Department, e.hiredate "Date_Hired" FROM emp e, dept d WHERE d.deptno = :P1 AND e.deptno = d.deptno; SET AUTOTRACE TRACEONLY: 9

10 Need Table & Index Info Understand objects in execution plans. Table & Segment sizes Number of Rows Indexes & their column order Column data types Cardinality of columns / Data Skew Statistic Gathering Histograms? Use TuningStats.sql Run it for expensive data access targets 10

11 Table & Column Statistics SELECT column_name, num_distinct, num_nulls, num_buckets, density, sample_size FROM user_tab_columns WHERE table_name = EMP ORDER BY column_name; SELECT count(*) FROM EMP; COUNT(*) SELECT 6013/4 dist FROM DUAL; DIST SELECT DEPTNO, count(*) FROM EMP GROUP BY DEPTNO; DEPTNO COUNT(*) Would an index on EMP.DEPTNO increase performance?

12 Histograms exec dbms_stats.gather_schema_stats( -ownname => 'SCOTT', options => 'GATHER AUTO', estimate_percent => dbms_stats.auto_sample_size, method_opt => 'for all columns size auto... exec dbms_stats.gather_table_stats( ownname => 'SCOTT', tabname => 'EMP', method_opt=>'for COLUMNS deptno SIZE 2'); 12

13 Extra Info - Bind Values V$SQL_BIND_CAPTURE STATISTICS_LEVEL = TYPICAL or ALL Collected at 15 minute intervals SELECT name, position, datatype_string, value_string FROM v$sql_bind_capture WHERE sql_id = '0zz5h1003f2dw ; NAME POSITION DATATYPE_STRING VALUE_STRING :P1 1 VARCHAR2(128) 40 EMP Columns: Name Type EMPNO NUMBER(4) ENAME VARCHAR2(10) JOB VARCHAR2(9) MGR NUMBER(4) HIREDATE DATE SAL NUMBER(7,2) COMM NUMBER(7,2) DEPTNO NUMBER(2) 13 Bind Values also provided by tracing Level 4 bind values Level 8 wait information Level 12 bind values and wait information

14 Execution Plan Details SELECT e.empno EID, e.ename "Employee_name, d.dname "Department, e.hiredate "Date_Hired" FROM emp e, dept dwhere d.deptno = :P1 AND e.deptno = d.deptno; Actual Plan: V$SQL_PLAN using dbms_xplan.display_cursor 14

15 Plans Not Created Equal SELECT company, attribute FROM data_out WHERE segment = :B1 Wait Time 100% on db file scattered read Plan from EXPLAIN PLAN Plan from V$SQL_PLAN using DBMS_XPLAN 15

16 Execution Plans Can Change With Oracle optimizer, execution plans can change as the underlying inputs to the optimizer change. Same Sql Different Schemas Same schema changes i.e. adding / dropping indexes Same Sql Different Costs Data volume & Statistic Changes over time Bind variable types and values Initialization parameters (set globally or session level) V$SQL_SHARED_CURSOR Can give clues to why plan changed Approximately 60 columns showing mismatches /differences 16

17 Tuning List How to Find the Expensive Operators Examine Costs / Row Count / Time Table Access Full? Review Filter and Access Predicates Shows how query is interpreted, e.g. bind variables Can help Diagnose Data Type Issues Evaluate Object Stats Table Definitions Sizes and Row Counts Determine Existing Indexes Index Definitions Index Selectivity Evaluate Column Stats Limiting Factors from WHERE Clause 17 Review Join Columns Are they indexed / data scew?

18 Example SQL Statement Find inventory of products in a specific category at a particular location? SELECT PRODUCTS.PRODUCT_ID, PRODUCT_NAME, PRODUCT_DESCRIPTION,CATEGORY_ID, WEIGHT_CLASS, WARRANTY_PERIOD, SUPPLIER_ID, PRODUCT_STATUS, LIST_PRICE,MIN_PRICE, CATALOG_URL, QUANTITY_ON_HAND FROM PRODUCTS, INVENTORIES WHERE INVENTORIES.PRODUCT_ID = PRODUCTS.PRODUCT_ID AND PRODUCTS.CATEGORY_ID = :B3 AND INVENTORIES.WAREHOUSE_ID = :B2 AND ROWNUM < :B1 ; Average Execution Time seconds Wait Event Waits 90% on direct path read 18

19 19 Why this SQL Statement?

20 Actual Plan SELECT. columns FROM PRODUCTS, INVENTORIES WHERE INVENTORIES.PRODUCT_ID = PRODUCTS.PRODUCT_ID AND PRODUCTS.CATEGORY_ID = :B3 AND INVENTORIES.WAREHOUSE_ID = :B2 AND ROWNUM < :B1

21 Actual Plan No Statistics SELECT. columns FROM PRODUCTS, INVENTORIES WHERE INVENTORIES.PRODUCT_ID = PRODUCTS.PRODUCT_ID AND PRODUCTS.CATEGORY_ID = :B3 AND INVENTORIES.WAREHOUSE_ID = :B2 AND ROWNUM < :B1

22 Understanding the Objects PRODUCTS View No Statistics DBMS_STATS Improved in 11g

23 Actual Plan With Statistics

24 How to tune? SELECT. columns FROM PRODUCTS, INVENTORIES WHERE INVENTORIES.PRODUCT_ID = PRODUCTS.PRODUCT_ID AND PRODUCTS.CATEGORY_ID = :B3 AND INVENTORIES.WAREHOUSE_ID = :B2 AND ROWNUM < :B1 ; V$SQL_BIND_CAPTURE NAME POSITION DATATYPE_STRING VALUE_STRING :B3 1 NUMBER category_id :B2 2 NUMBER warehouse_id :B1 3 NUMBER 15 - rownum INVENTORIES Table Filter (warehouse_id=454) records select round((1000 / * 100), 2) pct_of_inventory from dual; PCT_OF_INVENTORY

25 How to tune? SELECT. columns FROM PRODUCTS, INVENTORIES WHERE INVENTORIES.PRODUCT_ID = PRODUCTS.PRODUCT_ID AND PRODUCTS.CATEGORY_ID = :B3 AND INVENTORIES.WAREHOUSE_ID = :B2 AND ROWNUM < :B1 ; V$SQL_BIND_CAPTURE NAME POSITION DATATYPE_STRING VALUE_STRING :B3 1 NUMBER category_id PRODUCT_INFORMATION Table Filter (category_id = 136) 6 records USER_TAB_HISTOGRAMS

26 New Plan CREATE INDEX inventories_ix1 ON inventories(warehouse_id); 100% on CPU

27 Did performance improve? CREATE INDEX inventories_ix1 ON inventories(warehouse_id);

28 Which is the better Plan?

29 View using Display Plan EXPLAIN PLAN SET STATEMENT_ID = 'inventory' FOR SELECT PRODUCTS.PRODUCT_ID, PRODUCT_NAME, PRODUCT_DESCRIPTION,CATEGORY_ID, WEIGHT_CLASS, WARRANTY_PERIOD, SUPPLIER_ID, PRODUCT_STATUS, LIST_PRICE,MIN_PRICE, CATALOG_URL, QUANTITY_ON_HAND FROM PRODUCTS, INVENTORIES WHERE INVENTORIES.PRODUCT_ID = PRODUCTS.PRODUCT_ID AND PRODUCTS.CATEGORY_ID = :B3 AND INVENTORIES.WAREHOUSE_ID = :B2 AND ROWNUM < :B1; set pages 0 head off set linesize 132 set long col xplan format a100 spool inventory.html SELECT dbms_xplan.display_plan(statement_id => 'inventory',type=>'html') AS XPLAN FROM dual; spool off;

30 View using Display Plan

31 Free Graphical Plans 31

32 Free Graphical Plans

33 Summary Execution Plans show the internal steps Oracle takes to run SQL statements Reports how the data is accessed, manipulated and joined Shows Expensive steps with Cost and Time spent. Gives information on Bind Variables (predicate information) Viewing actual plans are better then using EXPLAIN PLAN V$SQL_PLAN using DBMS_XPLAN.display_cursor( &sql_id, 0) Tracing / TKPROF Gather additional data when tuning an execution plan Table sizes, Index selectivity and column details How Statistic Gathering is performed Bind value from V$SQL_BIND_CAPTURE Tune only the execution plans that make a difference Monitor response time Using Ignite 33

34 Tuning Aids DBMS_XPLAN Table Functions New Additions 11g SQL Plan management (DBMS_SPM) Free For Enterprise users Oracle - Note: requires Tuning/Diagnostic Packs SQL Tuning Advisor ADDM

35 DBMS_XPLAN Functions New Functions 11g BUILD_PLAN_XML Return the last plan, or a named plan, explained as XML DISPLAY Shows the last plan explained EXPLAIN PLAN ** Only FUNCTION in Oracle 9i DISPLAY_AWR DISPLAY_CURSOR DISPLAY_PLAN DISPLAY_SQLSET DISPLAY_SQL_PLAN_BASELINE FORMAT_NUMBER FORMAT_NUMBER2 FORMAT_SIZE FORMAT_SIZE2 FORMAT_TIME_S PREPARE_PLAN_XML_QUERY PREPARE_RECORDS VALIDATE_FORMAT Format & display the plan of a stored SQL statement in AWR Format & display the execution plan of any loaded cursor Return the last plan, or a named plan, explained as a CLOB Format & display the execution plan of statements stored in a SQL tuning set Displays one or more plans for the specified SQL statement Returns a number as a string Returns a number as a string formatted with a leading space (CHR(32)) Undocumented Undocumented Undocumented - function to build the XML version of a select query that is run before the display function to retrieve and display the execution plan of a SQL Used Internally Used Internally 35

36 DBMS_XPLAN Example EXPLAIN PLAN set statement_id = pri for select SELECT dbms_xplan.build_plan_xml(statement_id => pri ) AS XPLAN FROM dual; In browser: file:///c:/users/jgriffin/explan/xml.xml 36

37 SQL Plan Management 11g DBMS_SPM manages execution plans & ensures only known or verified plans are used ALTER_SQL_PLAN_BASELINE CONFIGURE CREATE_STGTAB_BASELINE DROP_SQL_PLAN_BASELINE EVOLVE_SQL_PLAN_BASELINE LOAD_PLANS_FROM_CURSOR_CACHE LOAD_PLANS_FROM_SQLSET PACK_STGTAB_BASELINE UNPACK_STGTAB_BASELINE Changes an attribute of a single plan or all plans associated with a SQL statement using the attribute name/value format Set configuration options for the SQL Management Base (SMB) as well as the maintenance of SQL plan baselines Creates a staging table that will be used for the purpose of transporting SQL plan baselines from one system to another Drops a single plan, or all plans associated with a SQL statement Evolves SQL plan baselines associated with one or more SQL statements Loads one or more plans present in the cursor cache for a SQL statement Loads plans stored in a SQL tuning set (STS) into SQL plan baselines Packs (exports) SQL plan baselines from SQL management base into a staging table Unpacks (imports) SQL plan baselines from a staging table into SQL management base 37

38 OEM Tuning Advisor Without Statistics With Statistics 38

39 Manual Run - 10g/11g column sql_id new_value sql_id select sql_id from v$sql where hash_value = &hash_value; DECLARE l_sql_tune_task_id VARCHAR2(100); BEGIN l_sql_tune_task_id := DBMS_SQLTUNE.create_tuning_task ( sql_id => '&sql_id', scope => DBMS_SQLTUNE.scope_comprehensive, time_limit => 60, task_name => '&sql_id', description => 'Tuning task for statement 19v5guvsgcd1v.'); DBMS_OUTPUT.put_line('l_sql_tune_task_id: ' l_sql_tune_task_id); END; / EXEC DBMS_SQLTUNE.execute_tuning_task(task_name => '&sql_id'); SET LONG 10000; SET PAGESIZE 1000 SET LINESIZE 200 SELECT DBMS_SQLTUNE.report_tuning_task('&sql_id') AS recommendations FROM dual; SET PAGESIZE 24 exec DBMS_SQLTUNE.drop_tuning_task (task_name =>'&sql_id');

40 Advisor Recommendations

41 Sql Tuning Advice - New index contains same columns but reversed.

42 OEM ADDM With Statistics 42

43 ADDM Commands-11g only 10g, must run the addmrpt.sql in?/rdbms/admin) var tname VARCHAR2(60); prompt Enter Start Date (mm/dd/yy hh24) accept beg_time prompt Enter End Date (mm/dd/yy hh24) accept end_time DECLARE bsnap NUMBER; esnap NUMBER; BEGIN select distinct BEGIN_SNAP_ID,END_SNAP_ID into bsnap,esnap from WRI$_ADV_ADDM_TASKS where BEGIN_TIME between to_date('&beg_time', 'mm/dd/yy hh24') and to_date('&end_time', 'mm/dd/yy hh24'); :tname := 'ADDM: ' bsnap '-' esnap; DBMS_ADDM.ANALYZE_DB(:tname, bsnap, esnap); END; / SET LONG SET PAGESIZE SELECT DBMS_ADDM.GET_REPORT(:tname) FROM DUAL;

44 ADDM Example Current Hour Example of ADDM Out put Analysis for current hour. Specific findings and suggestions